1. Field of the Invention
This invention relates to an apparatus for processing image data to enlarge and contract an image represented by the data. This invention also relates to a method of processing image data to enlarge and contract an image represented by the data.
2. Description of the Prior Art
It is well-known to use interpolation in processing image data to enlarge and contract an image represented by the data. Japanese published unexamined patent application 63-282886 discloses interpolation designed for such a purpose.
According to the interpolation disclosed by Japanese patent application 63-282886, each of areas among pixels of a whole original-image (source-image) region is divided into small segments or sub areas, and reference tables contain information of determining which of adjacent pixels should be selected for each sub area. The total number of the reference tables corresponds to the number of different combinations of pieces of adjacent-pixel information. The reference tables are provided in a ROM. For each pixel which will occur after an enlarging/contracting process (a pixel of an enlargement/contraction-resultant image or an object image), a corresponding original-image sub area is determined, and a reference table is selected which corresponds to a combination of adjacent pixels of the sub area. Then, information of determining which of the adjacent pixels should be selected in accordance with the sub area is read out from the reference table. Data of the adjacent pixel which is selected according to the information is written into a memory as pixel data representing a segment of the enlargement/contraction-resultant image.
The interpolation disclosed by Japanese patent application 63-282886 has a problem as follows. In the case of enlargement/contraction with an arbitrary magnification, for each pixel of an enlargement/contraction-resultant image, a corresponding original-image sub area needs to be determined. In addition, for each determined sub area, it is necessary to perform access to the ROM to select a reference table corresponding to a combination of adjacent pixels. In this way, an interpolating step is executed for each pixel of the enlargement/contraction-resultant image. Thus, in the case where such interpolating steps are required to be simultaneously executed on eight different pixels, it is necessary to simultaneously determine corresponding original-image sub areas for the eight pixels and also it is necessary to previously provide eight ROM's storing reference tables.
U.S. Pat. No. 4,933,775 discloses an image enlarging or contracting method which includes the steps of obtaining groups of interpolated image signal components along every array of original picture elements so that the interpolated picture elements corresponding to the interpolated image signal components of each group are deviated in position in a predetermined direction from the interpolated picture elements corresponding to the interpolated image signal components of every other group. A calculation is given of a mean value of the values of the interpolated image signal components corresponding to a set of the interpolated picture elements, which belong to different groups of the interpolated image signal components and which correspond to one another. The calculation of the mean value is repeated for every other set of the interpolated picture elements, thereby to ultimately obtain a group of the interpolated image signal components, which are to be used for image enlargement or contraction, along every array of the original picture elements.